1. Technical Field
The field of art of which this invention pertains may be generally located in the class of devices relating to measuring and testing apparatuses. Class 73, measuring and testing, U.S. Patent Office classification appears to be the applicable general area of art to which the subject matter similar to this invention has been classified in the past.
2. Background Information
It is known in the measuring and testing art to provide test apparatus for measuring the tightness of tanks, such as underground fuel storage tanks. U.S. Pat. No. 3,580,055 to Richard B. White discloses a test apparatus for measuring the tightness of tanks, particularly underground fuel storage tanks. The test apparatus shown in the said patent has concentric suction and discharge tubes which extend down through a fill pipe into the underground tank and a pump at ground level is connected to the upper end of those tubes to provide a continuous recirculation of the fuel out of and back into the tank. A temperature sensor is provided on the lower end of the suction tube. At ground level the apparatus has a calibrated stand pipe for controlling the hydrostatic pressure of the fluid in the tank. An adaptor sleeve extends part way down into the tank external fill pipe, around the outside of the suction tube. A radially expandable annular seal of short vertical extent is mounted on the outside of the adaptor sleeve and is operated by a handle at ground level to provide a seal between the adaptor sleeve and the inside of the fill pipe. The seal arrangement shown in said patent was not entirely satisfactory in many installations, and it had to be supplemented with a similar seal of larger diameter and other fittings. An attempt to overcome the disadvantages of the seal arrangement in U.S. Pat. No. 3,580,055 was described in a later U.S. Pat. No. 4,154,091. The seal arrangement disclosed in the last mentioned patent includes a flexible and resilient annular diaphragm, of an appreciable vertical length, clamped to the outside of an adaptor sleeve, above and below openings in the later. An inner sleeve extends down, with slight clearance, inside the adaptor sleeve and at their upper ends (at ground level) the space between them is connected to an air inlet valve. When pressurized air is introduced through this valve it forces the elongated annular diaphragm radially outward into fluid-tight sealing engagement with the inside of the fill pipe for the underground tank.
The seal arrangement in the last mentioned U.S. Pat. No. 4,154,091 has been found to have many disadvantages and it has a history of failure after only minimal usage. The air seal disclosed in the last mentioned patent is very hard to replace in the field and it has been found that factory repair is costly and time consuming. The last described air seal arrangement is limited for use with three and four inch diameter tank fill pipes. The failure history of said air seal shows that the use of such a seal arrangement is not commensurate with controlling pollution of the environment. Failure of such an air seal during a tank testing operation often results in a loss of flammable or toxic material to the environment. The pollution control agencies of the Federal and State governments are sensitive to the pollution of the environment, regardless of the circumstances, and the failure of a tank testing air seal during a tank tightness test could result in an expensive clean-up procedure.